The present invention is directed towards improvement in the speed of light sailing craft. First, there will be a brief discussion of the relationships involved in the propulsion of a sailboat.
FIG. 1 shows the relationship between the true wind velocity V.sub.T, at angle .gamma. to the boat velocity V.sub.B, and the apparent wind V.sub.A which the boat encounters. V.sub.A is the vector resultant of V.sub.T and -V.sub.B, the induced velocity of the boat. It meets V.sub.B at an angle .beta.. Replacing the vectors in FIG. 1 by their scalar magnitudes and applying the law of sines, it can be shown that EQU V.sub.B /V.sub.T =sin.gamma.ctn.beta.-cos.gamma.
However experience has shown that V.sub.B /V.sub.T, the ratio of boat speed to true wind speed, is maximum when the true wind V.sub.T is approximately on the beam, which is to say that .gamma..apprxeq.90.degree.. For this condition it can be shown that EQU V.sub.B /V.sub.T .apprxeq.cot.beta.
as shown in FIG. 2. It is evident that V.sub.B will not exceed 28 knots unless the boat is operated in a moderate gale or higher or unless .beta. can be reduced so that EQU V.sub.B /V.sub.T &gt;1
From the velocity triangle it can also be shown that V.sub.A /V.sub.T, the ratio of apparent wind speed (which later will be shown to be of crucial importance) to true wind speed is maximum at .gamma.=90.degree. and increases as .beta. decreases. In brisk winds, however, if .beta. is reduced so that V.sub.A approaches the course direction, a very large transverse force, with accompanying large overturning moment, ensues and there results an increase in drag due to heel and due to the increased displacement that arises from the downward reaction of a sail inclined to leeward.
The resistance of a hull can be reduced if its displacement or its wetted surface is reduced. Both of these reductions can be achieved if the craft is lifted out of the water. Planing craft and hydrofoil craft exemplify the usual approach to this end; however, lifting can be accomplished more efficiently if aerodynamic, rather than hydrodynamic, means are used. The herein described invention combines aerodynamic propulsion, aerodynamic lifting and aerodynamic neutralization of moments to yield a sailing vessel of enhanced speed capability.